Method of stabilizing composite media and media produced thereby

ABSTRACT

A composite media comprising a backing sheet, a covering sheet, and a layer disposed between said backing sheet and said covering sheet, said layer having particles of active ingredient, binder particles, and stabilizing particles, wherein the active particles are coalesced by the binder particles, wherein each of the stabilizing particles bonds with both the backing sheet and the covering sheet, and wherein the stabilizing particles are larger than the binder particles.

This application is a continuation-in-part of co-pending U.S. patentapplication No. 08/903,395, filed Jul. 22, 1997, U.S. Pat. No. 6,077,588, which is a division of U.S. patent application Ser. No. 08/813,055,filed Mar. 7, 1997 and issued as U.S. Pat. No. 5,792,513.

FIELD OF THE INVENTION

The present invention relates generally to activated media. Moreparticularly, the present invention relates to a method of stabilizingactivated media and media produced thereby.

BACKGROUND OF THE INVENTION

It is often desirable to impregnate, cover, or otherwise treat a basematerial with an active or activated material, such as an absorbent oradsorbent material. One example would be a non-woven medium coated withagents having fluid adsorption and/or odor adsorption characteristics,as found in children's diapers, adult incontinence products, femininehygiene products, and other adsorbent articles of clothing. Otherexamples include coated paper tissues and toweling, as well as surgicalbandages and sanitary napkins. Other materials may be used as adsorbentmaterials, such as cyclodextrins or zeolites for odor control, or otheradsorbents such as silicates, aluminas, or activated carbons.

The active, i.e., adsorbent, materials used to coat a base material maybe fibrous or particulate materials. However, certain materials known inthe art (e.g., fluff pulp fibers) have limited adsorption capacity, andhence perform disappointingly during normal wear. In addition, productscontaining such materials are often heavy and/or bulky. Thus, it ispreferable to use at least some portion of particles composed of superadsorbent polymers (SAP).

Yet, it is difficult to immobilize powdered or small granular particlesof SAP. Historically, microscopic active materials were immobilized onfoams or on surfaces coated with a thin layer of pressure-sensitiveadhesive. U.S. Pat. No. 5,462,538 to Korpman is an example of a methodof immobilizing adsorbent material on a surface coated with a thin layerof pressure-sensitive adhesive. Using this method may produce large gapsbetween individual microscopic adsorbent elements. Also, the resultingadsorbent core has only a single layer of adsorbent material. PCTPublication No. WO 94/01069 to Palumbo is another example of a method ofimmobilizing particulate adsorbent material. However, the adsorbentparticles are not bonded to the substrates. Moreover, the adsorbentparticles are not in significant contact with the binder particles.Thus, neither method effectively restrains powdered or small granularparticles of an active ingredient.

As a more effective alternative, U.S. Pat. No. 5,792,513, which is fullyincorporated herein by reference, discloses a product formed from acomposite mixture of adsorbent particles and binder particles fused to asubstrate. While this product provides excellent absorptioncharacteristics, the particles swell when exposed to fluid and thenseparate from the substrate and each other during normal use. This loosematerial is then free to slump or move.

In light of the foregoing, there remains a need for media, and a methodof producing such media, in which the particles of an active ingredientare substantially immobilized even after they have become swollen, whilemaintaining excellent composite integrity.

SUMMARY OF THE INVENTION

The present invention provides an improved composite medium, in whichthe particles of an active ingredient are substantially immobilized. Afurther object is to provide absorbent or adsorbent articles havingstabilizing particles dispersed throughout a coalesced composite layerof particles of an active ingredient and binder particles. Bysubstantially immobilizing the particles of an active ingredient thepresent invention effectively prevents migration of the particles of anactive ingredient, thereby creating an adsorbent product with enhancedintegrity throughout the use cycle of the product.

Accordingly, the present invention provides composite media and a methodof producing them. The composite media contain a coalesced compositemixture of particles of an active ingredient and binder particles. Thebinder particles preferably also fuse the composite structure to frontand back substrates. The composite media also have stabilizing particlesthat fuse with both the particles of the active ingredient and thesubstrates, thereby forming a composite medium according to the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side plan-view of the composite media of the presentinvention; and

FIG. 2 is a schematic diagram illustrating an apparatus for the practiceof the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings and, in particular, FIG. 1, there is provideda composite medium generally indicated as 1. Composite medium 1 has abacking substrate 10 and a covering substrate 20.

Backing substrate 10 and covering substrate 20 may be formed of variousmaterials depending upon the application. By way of example, substrates10, 20 may be a permeable material, such as a non-woven fibrousmaterial, e.g., spun-bonded polyester or polyolefin. Woven substratesmay also be used. Furthermore, substrates 10, 20 may optionally beformed using cellulosic materials, such as paper, or a combination ofcellulosic and thermoplastic fibers. Either substrate 10 or 20 may alsobe an impermeable material, such as a plastic film (e.g., Mylar®), apermeable backsheet or membrane or another suitable material.

The particular material selected for substrates 10, 20 can also effectthe kinetics of adsorption of composite medium 1. For example,substrates 10, 20 can modify the mean pore size and the overallporosity, provide supplemental adsorption, improve tensile strength,flexibility, and pleatability, and effect wicking and fluiddistribution.

Between substrates 10, 20, there is a layer, generally indicated as 2.Layer 2 has particles of an active ingredient 30, binder particles 40,and stabilizing particles 50. Particles of an active ingredient 30 arecoalesced or fused together by binder particles 40. An amount of binderparticles 40 may also be fused to points on either substrates 10 or 20,thereby also binding particles 30 to substrates 10 and 20. However,binding particles 40 will only be fused with one of substrates 10 and20, rather than both. Stabilizing particles 50 may also be bonded toparticles of an active ingredient 30 and, in contrast to bindingparticles 40, are fused to both backing substrate 10 and coveringsubstrate 20, thereby forming a stabilizing bond or quilting effect.

In other words, as shown in FIG. 1, because of their smaller size, eachbinding particle 40 may bind to either substrate 10 or substrate 20, butnot both, or to neither of substrates 10 and 20.

The thickness of layer 2 will vary depending on a variety of factors,including the size of the particles 30, 40, and 50, the quantity ofparticles 30, 40, and 50, the degree of coalescence between particles30, 40, and 50, and whether other particles or fibers, such as fluffpulp, are used in layer 2. Preferably, the thickness of layer 2 is about0.2 mm to about 5 mm.

Particles of an active ingredient 30 can potentially be formed of anymaterial. For example, particles of an active ingredient 30 may absorbor adsorb fluids or gases. Furthermore, particles of an activeingredient 30 may be used to release fluids or gases held therein, forexample, to deliver fluids, such as medicaments. Materials such asiodinated resin, activated carbon, activated alumina, aluminum powders,nickel powders, alumina-silicates, ferromagnetic materials, ion-exchangeresins, manganese or iron oxides, zeolites, glass beads, ceramics,diatomaceous earth, and cellulosic materials can also be used asparticles of an active ingredient 30. In addition, particles of anactive ingredient 30 may also be polymeric materials, such as SAP. Thecross sectional size of particles of an active ingredient 30 ispreferably within a range of about 5 microns to about 5000 microns.

Materials forming binder particles 40 may potentially include anymaterial known in the art. In particular, thermoplastic and thermosetmaterials are useful for the practice of the present invention. Forexample, binder particles 40 may be polyethers, polyolefins, polyvinyls,polyvinyl esters, polyvinyl ethers, ethylene-vinyl acetate copolymers,or a mixture thereof. Also, suitable binder particles may be producedfrom particulate thermoset resins known in the art, such asphenol-formaldehyde or melamine resins, with or without additionalcrosslinking agents. Preferably, binder particles 40 are present in suchan amount and at such a size that they do not substantively interferewith the functioning of particles 30. Binder particles 40 are preferablyabout 5 microns to about 50 microns in size.

The critical feature of this invention resides in stabilizing particles50 that are used to form through-web stabilizing bonds within layer 2.First, stabilizing particles 50 perform a similar function as binderparticles 40, specifically coalescing or fusing together particles of anactive ingredient 30. However, they are extremely limited in theircapacity to stabilize the active ingredient particles because they arelarge and provide limited surface area to interface with the activeingredient and they are generally present in small amounts, againlimiting their ability to stabilize other particles. Stabilizingparticles 50 are also adhered or fused to both substrates 10, 20 becausethey are selected to have a particle size roughly equal to or greaterthan the thickness of layer 2. Materials forming stabilizing particles50 are potentially any suitable material, such as the materials listedin reference to binding particles 40, e.g., a thermoplastic or athermoset material. Stabilizing particles 50 are preferably present insuch an amount and at such a size that they do not substantivelyinterfere with the functioning of particles of an active ingredient 30and binder particles 40. It is preferred that stabilizing particles 50be both larger in size and fewer in number compared to binder particles40. Preferably, stabilizing particles 50 are equal to or larger than thethickness of layer 2, so as to allow stabilizing particles 50 to spanthe entire thickness of layer 2 and directly adhere to substrates 10,20. However, stabilizing particles may be smaller than the thickness oflayer 2, for instance, if a ribbed effect for composite medium 1 isdesired. In addition, stabilizing particles may be intimately groupedtogether, thereby binding to both substrates 10, 20 in the aggregate.

FIG. 2 illustrates an exemplary apparatus for the practice of thisinvention. A supply roll 100 provides a substrate 120 to be treated,such as a nonwoven tissue or toweling paper. Downstream from supply roll100 is a knurled roller 130 positioned to receive a mixture of particlesof an active ingredient 30, binder particles 40, and stabilizingparticles 50, the mixture generally being indicated as 140 and dispensedfrom a hopper 160. Mixture 140 is applied to the upper surface ofsubstrate 120 as a continuous coating or, alternatively, as a coating ofa specific design such as, for example, stripes. A brush 180 may beemployed to aid in removing mixture 140 from knurled roller 130.Thereafter, substrate 120 is passed through a nip 200 between a heatedidler roller 220 and a drive roller 240. Alternatively, before beingpassed through nip 200, substrate 120 may also be preheated, forexample, by a convection or infrared oven. A pneumatic cylinder isconnected via a rod 280 to the axle of idler roller 220 to maintain adesired pressure on substrate 120 within nip 200. In passing over thesurface of heated roller 220, mixture 140 is heated to a temperatureequal to or greater than the softening temperature of binder particles40 and stabilizing particles 50, but lower than the softeningtemperature of particles of an active ingredient 30. Within nip 200,binder particles 40 and stabilizing particles 50 fuse under pressurewith particles of an active ingredient 30, while stabilizing particles50 also fuse with substrate 120. An amount of binder particles 40 mayfuse with substrate 120. Furthermore, in a preferred alternative to theabove described apparatus, a second supply roll 300 of a substrate 320,which may be of the same or a different material from that of substrate120, is also passed between nip 200 on the top of mixture 140.Stabilizing particles 50 fuse with substrate 320 and an amount of binderparticles 40 may also fuse with substrate 320. However, whilestabilizing particles 50 fuse with both substrate 120 and 320, binderparticles 40 will only fuse with either substrate 120 or 320. Uponleaving the nip 200, binder particles 40 and stabilizing particles 50cool and harden. The composite medium 240 passes onto a takeup roll 360.

Coalescing particles of an active ingredient 30 with interposed binderparticles 40 and stabilizing particles 50 results in more completecoverage of the backing substrate 10 and places particles of an activeingredient 30 in closer proximity to each other. In addition, it ispossible to vary the depth and porosity of layer 2 and to have multiplelayers of active ingredient fully stabilized by binder particles 40.When composite layer 1 contains SAP and is wetted, the SAP particlesswell and generally break their bonds with binder particles 40 and anybonds that might exist with stabilizing particles 50. However, the bondsbetween substrates 10 and 20 and stabilizing particles 50 are retainedand prevent the wholesale disassembly of composite layer 1. These stablebonds do not prevent local swelling of the composite layer 1, but doprovide localized stabilization of composite layer 1 at each point wherestabilizing particle 50 spans composite layer 1. These bonds provide arandom quilting effect that prevents the movement of the swollen SAPmass.

Although composite medium 1, and the method of producing such a medium,has been described with respect to one or more particular embodiments,it will be understood that other embodiments of the present inventionmay be employed without departing from the spirit and scope of thepresent invention.

Hence, the present invention is deemed limited only by the appendedclaims and the reasonable interpretation thereof.

What is claimed is:
 1. A composite medium comprising: a backing sheet; acovering sheet; and a layer disposed between said backing sheet and saidcovering sheet, said layer having particles of active ingredient, binderparticles, and stabilizing particles, wherein said active particles arecoalesced by said binder particles, and wherein each of said stabilizingparticles forms a bond with both said backing sheet and said coveringsheet, said stabilizing particles being of a size larger than saidbinder particles.
 2. The composite medium of claim 1, wherein saidbacking sheet is an impermeable material.
 3. The composite medium ofclaim 1, wherein said backing sheet is a permeable material.
 4. Thecomposite medium of claim 1, wherein said covering sheet is a permeablematerial.
 5. The composite medium of claim 1, wherein said layer has anaverage thickness of about 0.2 mm to 5 mm.
 6. The composite medium ofclaim 1, wherein said particles of an active ingredient are formed fromat least one component selected from the group consisting one of:adsorbent particles, absorbent particles, particles that release liquidor gases held therein, and mixtures thereof.
 7. The composite medium ofclaim 1, wherein said particles of an active ingredient are formed fromat least one component selected from the group consisting one of:iodinated resin, activated carbon, activated alumina, alumina-silicates,ion-exchange resins, manganese oxides, iron oxides, zeolites,hydrophilic polymeric materials, and mixtures thereof.
 8. The compositemedium of claim 1, wherein said particles of an active ingredient havean average particle size of between about 5 microns to 5000 microns. 9.The composite medium of claim 1, wherein said binder particles areformed from at least one component selected from the group consistingone of thermoplastic materials, thermoset materials, and combinationsthereof.
 10. The composite medium of claim 1, wherein said binderparticles are formed from at least one component selected from the groupconsisting of: polypropylene, linear low-density polyethylene, lowdensity polyethylene, ethylene-vinyl acetate copolymer, polyolefin,phenol-formaldehyde resin, melamine resin, and mixtures thereof.
 11. Thecomposite medium of claim 1, wherein said binder particles have anaverage particle size of between about 5 microns to 50 microns.
 12. Thecomposite medium of claim 1, wherein said stabilizing particles areformed from at least one component selected from the group consisting ofthermoplastic materials, thermoset materials, and combinations thereof.13. The composite medium of claim 1, wherein said stabilizing particlesare formed from at least one component selected from the groupconsisting of polypropylene, linear low-density polyethylene, lowdensity polyethylene, ethylene-vinyl acetate copolymer, polyolefin,phenol-formaldehyde resin, melamine resin, and mixtures thereof.
 14. Thecomposite medium of claim 1, wherein said stabilizing particles have aparticle size equal to or greater than the thickness of said layer. 15.The composite medium of claim 1, wherein said stabilizing particles arepresent in an amount and in a size so as to not interfere with thefunctioning of said active particles and said binder particles.
 16. Thecomposite medium of claim 1, wherein said stabilizing particles arefewer in number than said binder particles.
 17. The composite medium ofclaim 1, wherein said stabilizing particles are smaller than thethickness of said layer.
 18. The composite medium of claim 1, havingregions wherein several stabilizing particles group together to bind thebacking sheet and the covering sheet.
 19. The composite medium of claim1, wherein a portion of said binder particles also bind a portion ofsaid active particles to at least one of said backing sheet and saidcovering sheet.
 20. The composite medium of claim 1, wherein saidparticles of active ingredient comprise a super adsorbent polymer.